Size-dependent mortality in a Neotropical savanna tree: the role of height-related adjustments in hydraulic architecture and carbon allocation

Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than ∼6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO₂ assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance ( K _leaf) than small trees and all tree sizes exhibited lower K _leaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits.     

PROCESS OF FUNCTIONAL SEX REVERSAL OF THE GONAD IN THE FEMALE GUPPY, POECILIA RETICULATA, TREATED WITH ANDROGEN BEFORE BIRTH

In the guppy, Poecilia reticulata , ovarian differentiation occurs during the embryonal life by 14 days after the preceding parturition. Testicular differentiation begins with the appearance of prominent aggregations of stroma cells in the gonadal hilus occurring by 18 days following the last parturition.
Oral administration of methyltestosterone (400 μ/g diet) to gravid guppies, begun 13–15 days after the preceding parturition and continued until the end of gestation, induced a male-type aggregation of somatic cells in the hilus of ovaries of female embryos. Gonads of newly born, androgenized females still had developing oocytes but were always provided with atypical clusters of stroma cells in their hilus. The gonads of affected female offspring developed successively into definite testes within 20 days after birth, displaying a precocious differentiation of the hilar stroma into sperm ducts and testicular interstitium, a concomitant initiation of spermatogenesis, and a conspicuous degeneration of oocytes. A successful masculinization of the somatic element, which may occur prior to that of the germ cells, in androgen-affected embryonic ovaries seems to be essential for the functional sex reversal of genetic females in the guppy.     

Inhibitory Effects of Oxygen on the Germination of Oryza sativa L. Seeds

Some workers have reported that the breaking of seed dormancyin rice (O. sativa L.) is usually enhanced by higher oxygentension, whereas others have shown that rice seed dormancy canbe broken by incubation under anaerobic conditions. This articleaims to clarify this paradox. The results show that high oxygentensions inhibit seed germination for a certain period afterharvest in Japonica rice, whereas Indica rice cultivars arenot inhibited by oxygen at any stage. Oxygen inhibition, seed germination, aquatic plants, Japonica rice, Indica rice     

Inhibitory Action of an Imidazole Compound on Ecdysone Synthesis in Prothoracic Glands of the Silkworm, Bombyx mori

The precocious pupation was induced either by allatectomy at the time of third ecdysis or by topical application of an imidazole compound (KK-42; 1-benzyl-5-[( E )-2, 6-dimethyl-1, 5-heptadienyl] imidazole) to the fourth (penultimate) instar larvae of the silkworm, Bombyx mori. However, the critical period for KK-42 treatment in induction of precocious pupation was longer than that for allatectomy. The effects of KK-42 depended on the doses applied and a half-maximum dose was estimated to be approx. 10 μg/larva. KK-42 suppressed the increase in hemolymph ecdysteroid titres leading to larval ecdysis in controls. Ecdysteroid levels remained at low levels for about 6 days after the treatment, followed by an increase toward precocious pupation. When the prothoracic glands from the mature fifth instar larvac were incubated in vitro in Grace's medium containing various concentrations of KK-42, secretion of ecdysone into the medium was suppressed depending upon the doses of KK-42 added and a half-inhibition concentration was estimated to be approx. 1 nM. Thus, KK-42 was shown to be an inhibitory agent to ecdysteroid secretion in silkworm larvae.     

Histological Detection of Chicken δ-Crystallin DNA Sequences Introduced into Mouse Teratocarcinoma Cell Lines

In situ hybridization techniques to detect specific DNA sequences in histological sections were developed for the purpose of analyzing experimental chimeras produced by combination of mouse teratocarcinoma (TCC) cells stably carrying chicken δ-crystallin DNA sequences and normal mouse embryos. Various hybridization conditions for detection of exogenous DNA sequences were compared in samples of solid tumors of TCC lines. Of the conditions examined, denaturation of DNA in alkali and hybridization at 68°C in 6x SSC in the presence of dextran sulphate was the best for detecting δ-crystallin DNA sequences. With ³H-labelled probe under these conditions, virtually all nuclei containing more than 100 copies of chicken δ-crystallin sequences were labelled sufficiently to be distinguishable from nuclei without chicken sequences. This technique could be applied to other experimental chimeras in which specific DNA sequences can be used as markers of certain cell lineages.     

Reactivity of a Monoclonal Antibody Raised against Human Leukemic Cells to Embryonic and Adult Tissues of the Mouse and Teratocarcinomas

C-9-1, a monoclonal IgM antibody raised against human null cell acute lymphocytic leukemia cells reacted with restricted regions of embryonic and adult tissues of the mouse. The antigen positive sites in the embryos included embryonic ectoderm, visceral endoderm, trophoblastic cells invading the maternal decidua of 5∼7-day embryos, primordial germ cells of 10∼12-day embryos, epithelium of nasal chamber, the bronchus, Mullerian duct, epididymis and bladder of 12∼17-day embryos. In the adult mice, C-9-1 antigen was detected in renal tubules, a part of stomach, bladder, endometrium and epididymal sperm. Embryonal carcinoma cells, but not endodermal cells of teratocarcinoma expressed the antigen. Thus, C-9-1 antigen showed distribution similar to SSEA-1. However, C-9-1 antigen was not detected in preimplantation embryos, nor in oviduct, both of which are positive for SSEA-1.     

Changes of Some Mitochondrial Enzyme Activities of Cucumber Leaves during Ammonium Toxicity

The following enzyme activities were determined in the mitochondria of cucumber leaves (Cucumis sativus L. cv. Suisei No. 2) during ammonium toxicity: malate dehydrogenase, succinate dehydrogenase, glutamate dehydrogenase, cytochrome c oxidase, NADH diaphorase, NADH oxidase, succinate: cytochrome c oxidoreductase, NADH: cytochrome c oxidoreductase and adenosine triphosphatase. The activities of all enzymes except ATPase increased more or less during ammonium toxicity. Generally speaking the marked increase was found at 7 days treatment with 200 mg/1 NH₃-N. The adenosine triphosphatase activity of injured plants was lower than that of normal plants through treatment. The addition of various organic acids (15 mM) to the culture solution contaning 200 mg/1 NH₃-N (14.3 mM NH₄Cl) suppressed the ammonium toxicity. The accumulation of free ammonia in the leaves was also repressed by the addition of organic acids. The results of present and previous reports suggest that the increase of respiratory metabolism due to ammonium toxicity is required for the supply of organic acids, specially δ-ketoglutaric acid, to counteract ammonia. Uncoupling in mitochondria resulting in the increase of respiration does not seem to occur during ammonium toxicity.     

Macrophage Migration Inhibition by Serum from Desensitized Animals Previously Sensitized with Tubercle Bacilli

MIGRATION of peritoneal exudate cells removed from guinea-pigs or mice exhibiting delayed hypersensitivity is inhibited by specific antigen^1–3. This in vitro macrophage migration inhibition has been regarded as a useful immunological test for delayed skin hypersensitivity^4,5. Studies of the mechanism of this phenomenon revealed that, in contact with specific antigen, lymphocytes from sensitized animals released into the medium a specific substance (migration inhibitory factor; MIF) capable of inhibiting the migration of normal macrophages^6,7. When injected intradermally into normal guinea-pigs, MIF elicits inflammatory reactions characterized by induration, erythema and mononuclear cell infiltration⁸.     

Auxin-induced heritable variants in yeast with special reference to physiological and genetic characters

A high concentration (400 mg/l) of an auxin, -naphthaleneaceticacid produced heritable variants differing in cell form andsize and in sporulation ability in a diploid strain of Saccharomycescerevisiae. These variants showed altered absorption spectrain the region of cytochromes a + a₃, b and/or c, but could growin a glycerol medium. Cultures of dissected spores from thesevariants involved many non-maters. These variants showed irregularsegregation of nutritional markers and/or a high DNA contentper cell. Since most of the variants grow more slowly on anauxin medium than does the original strain, they seem to beproduced by the induction by auxin rather than by selectiveenrichment. Genetic control of the ability to respond to auxinand the biological significance of auxin-induced variation inyeast is discussed. (Received January 12, 1968; )     

Effects of after-ripening and gibberellic acid on the thermoinduction of seed germination in Solarium melongena

Daily alternating temperatures or a short exposure to low orhigh temperatures were necessary for the germination of eggplantseeds at the initial stage of after-ripening. But requirementsbecame less strict with the progress of after-ripening, andafter 4 to 8 months of afterripening, germination occurred easilyboth at constant (20 and 25) and daily alternating temperatures(30 for 16hrs and then 20 for 8hrs). With further progress in after-ripening, however, daily alternatingtemperatures or a short exposure to low or high temperaturesbecame again indispensable for attaining a high percentage ofgermination. The progress of after-ripening was greatly influencedby the degree of seed ripening, that is, by the period beforethe seeds were sampled from fruits after anthesis (ripening). The effect of GA on the germination of egg plant seeds varieddepending on the concentration of GA, temperature and the degreeof maturity (ripening and after-ripening) of the seeds. (Received March 8, 1968; )